1. Field of the Invention
The present invention relates to the production of novel stretchable elastomeric film elements which are rendered porous so as to have breathing properties but which also are provided with improved resistance to tearing if punctured while under the stress of being stretched during use.
Stretchable elastomeric films, such as of natural polymeric materials including natural rubber latex and synthetic polymeric materials including butadiene-styrene rubbers, isoprenes and a wide variety of other known elastomers, are well known for use in various applications where porosity is imparted in order to render the films air-permeable or breathable. Most such applications relate to the use of the stretchable films as garments or protective or therapeutic coverings for parts of the human body, such as girdles, swim caps, scuba garments, compressive medical cast coverings, bandages, diaper components, etc. An elastomer is a material which can be stretched at room temperature to at least twice its original length, held for 5 minutes and, upon release, will return to within 10% of its original length within 5 minutes.
2. Discussion of the Prior Art
Conventionally, stretchable elastomeric films have been rendered air-permeable or breathable by mechanical die cutting, punching or perforating machines having circular cutting elements, dies or punchers of predetermined diameter and spacing which cut through the elastomeric films to remove portions thereof and produce air-permeable holes having the desired diameter and spacing.
While such mechanically-cut holes or perforations impart the desired air-permeability and breathing properties to the elastomeric film materials, they have the disadvantage of substantially increasing the tendency of the elastomeric film to tear each time that the film is stretched, such as during application and removal of a garment. Applicant has discovered that such weakness of the perforated elastomeric film is due to the inherent formation of minute irregularities, cuts, tears or abrasions on the walls of the air passages or holes punched through the elastomeric film. While such irregularities generally are not visible to the unaided eye and do not detract from the appearance or breathing properties of the elastomeric film, they represent a plurality of weakness points when the elastomeric film is stretched or elongated to several times its static length and/or width, particularly with high localized finger pressure and/or finger nail pressure. When the stretched film tears at one perforation the tear quickly propagates through adjacent perforations since each perforation has wall weaknesses.
It is known to form perforations in a variety of materials, such as paper, plastic conduits and plastic films, by means of high intensity laser devices to control the porosity of the materials. Reference is made to U.S. Pat. Nos. 3,226,527; 3,617,702; 4,028,525; 4,032,743; 4,218,606; 4,672,168 and 4,743,123 for their disclosures of conventional laser perforation devices and their use for forming laser perforations in a variety of materials, including thin plastic films. None of these references disclose the formation of perforations in stretchable elastomeric films or the formation of laser-perforated plastic films which are more resistant to tearing than corresponding films which are mechanically-perforated.